For automatic cleaning of the tubes of a tube hear exchanger, the main stream of fluid traversing same can be charged with cleaning elements, e.g. foam-rubber balls, which are carried along with the main stream and scour the inner surfaces of the tube. It is necessary to recover the cleaning elements from the main stream downstream of the tubes and to recycle them to the oncoming main stream upstream of the tubes.
A system of this type is described, for example, in U.S. Pat. No. 3,021,117. Generally a device of this type for recovering the cleaning elements from the main stream comprises a vertically exposed cylindrical duct having a circular cross section and formed internally with a separating sieve or grate which is inclined to the axis of the duct so that the separating disk or sieve has a generally elliptical periphery.
In one arrangement of this type, (see German published application- Auslegeschrift DTAS No. 1,303,750), the separating device comprises a box-like housing provided on a horizontal lower edge of the separating sieve or grate and having a pair of parallel vertical side walls with grate-like members forming a wedge, i.e. converging toward one another. As a rule, two separating sieves are provided symmetrically to feed into the box-like discharge structure.
A problem has been found to arise with such systems in that the velocity of the gas must be carefully controlled to prevent accumulation of the particles, balls or other cleaning elements upon the grates and the jamming of the discharge device. This effect is especially pronounced at high throughflow velocities.